Mr Pronk's personal website is well known among UN officials and they have repeatedly asked him to stop writing it, our correspondent says.

"Morale in the government army in north Darfur has gone down," he wrote. "Some generals have been sacked; soldiers have refused to fight."

He said the Sudanese army had lost two major battles recently to rebel groups in the western region and that Arab militias - who have been accused of atrocities - were being mobilised in violation of UN resolutions.

The army led calls for Mr Pronk's expulsion, calling his remarks psychological warfare.

Junior Foreign Minister Sammani al-Wasila told the BBC that Mr Pronk had strayed beyond his mandate and lost his neutrality.

"It is not his right to comment," he said. "His role as personal envoy to the secretary general means he should be neutral to help solving problems, rather than creating problems."